1. Field of the Invention
The present invention relates to method and apparatus for detecting a stroke of a 4-cycle engine. More particularly, the present invention relates to method and apparatus of the type described, which enhances accuracy of stroke detection in an operational region having a low rotary engine speed and a large throttle opening.
2. Description of the Background Art
There is a known 4-cycle internal combustion engine having a control device (including stroke detection apparatus) for determining optimum ignition timing. This type of known engine is described, for example, in published Japanese patent document JP-A-2007-182797. In the single-cylinder 4-cycle engine disclosed by this reference, an intake manifold vacuum changes over time, in a region where a rotary speed of the engine is low and a throttle opening is small.
In other words, although an upward peak appears in an intake vacuum waveform in a region extending from an exhaust stroke to an intake stroke of the engine, the upward peak does not appear in a region extending from a compression stroke to a power stroke. Accordingly, conventionally, the stroke detection is performed based on monitoring changes in the intake manifold vacuum.
However, there may be a situation in which the stroke detection based on such intake manifold vacuum cannot be performed. For example, in a motorcycle which performs off-road traveling, there may be a case when rotation of a rear wheel is instantaneously stopped by applying a full-braking operation to a rear wheel or the like. Here, the rotation of a crankshaft is also instantaneously stopped. Hence, a stage which is allocated to each predetermined crank angle cannot be recognized by reference to changes in intake manifold vacuum.
Accordingly, when the rear-wheel brake is released thereafter, so that the rear wheel is rotated and a traveling state of the motorcycle is resumed to normal traveling, it is necessary to quickly determine a stroke and a crank reference position for every crank angle of 360°. When a throttle is opened widely for accelerating quickly to a normal traveling speed, the crank angle reference position can be determined, but the intake manifold vacuum is hardly changed due to the open throttle, and the intake vacuum is temporarily brought into a flat, unchanged state. Hence, the stroke detection based on the intake manifold vacuum cannot be performed, whereby there may be a possibility that the engine cannot provide peak performance.
Alternatively, the stroke detection may be performed based on other information besides a change in the intake manifold vacuum.
For example, there is a known method of stroke determination, disclosed in the Japanese patent document JP-A-2007-182797, which detects a crank pulse period in a crank stage including a top dead center position. The method of this reference determines a currently-performed stroke as a compression stroke when a detected period is longer than a reference period, and determines the currently-performed stroke as an exhaust stroke when the a detected period is shorter than a reference period. According to the stroke determination method as disclosed in the Japanese patent document JP-A-2007-182797, it is possible to perform the stroke detection during approximately one rotation of the crank after starting the engine.
Further, the Japanese patent document JP-A-2004-124879 discloses a stroke detection method used in a single-cylinder engine which performs stroke detection by equally dividing two rotations of the crank, that is, one cycle in four, by measuring a time for every ¼ cycle, and by recognizing a change pattern of a crank angular velocity.
Also, the Japanese Patent No. 2541949 discloses a stroke detection method for a single-cylinder engine, which performs the stroke detection by comparing rotary speeds at positions before and after a top dead center orientation of the crankshaft.
However, in the method disclosed in the Japanese patent document JP-A-2007-182797, the crank pulse period is compared with the reference period. Hence, the method is not applicable to various starting variations such as kick starting or cell starting, whereby there may be a possibility that the stroke detection cannot be performed in such conditions.
Further, in the methods disclosed in the Japanese patent document JP-A-2004-124879 and the Japanese Patent No. 2541949, although the change of the angular velocity sufficient for performing the stroke detection can be acquired in a low-rotary speed range where the change of rotation during one cycle is large, the change of rotation during one cycle is small in a high-rotary speed range. Hence, there exists a possibility that the change of an angular velocity sufficient for performing the stroke detection cannot be acquired. Accordingly, it is desirable to enlarge a region where the stroke detection can be performed.
The present invention has been made to overcome such drawbacks of existing stroke determination methods and apparatus. Accordingly, it is one of the objects of the present invention to provide a method and apparatus for stroke detection of a 4-cycle engine which can overcame the above-mentioned drawbacks of the known art, and which can perform stroke determination in an enlarged determination region. Particularly, it is an object of the present invention to provide a method and apparatus for a stroke detection apparatus of a 4-cycle engine, which is capable of detecting the stroke with a high accuracy in an operation region where a rotary speed of the engine is low, and a throttle opening is large.